A procedure was devised for producing double-stranded DNA sequences corresponding to each of the influenza virus RNA segments. Negative and positive strands of influenza RNA segments were copied separately into DNA using the reverse transcriptase of avian myeloblastosis virus. The DNA products of the reverse transcriptase enzyme appeared to represent full-length genomic copies. The single-stranded DNA molecules from both preparations were annealed to generate double-stranded DNA segments which were subsequently isolated for cloning in plasmid PBR322 of E. coli K-12. The in vitro synthesized double stranded influenza DNA segments were then inserted into plasmic PBR322 at the specific Pst I site using the dG-dC tailing technique. The hybrid DNA molecules were used to transform recipient E. coli and transformants containing influenza gene sequences were identified by hybridization. In this manner, we have so far obtained putative full-length influenza virus DNA segments corresponding to genes coding for non-structural protein (Gene VIII), matric protein (gene VII), neuraminidase (gene VI), and hemagglutinin (gene IV). Cloning of other genes from wild type influenza A/Udorn/72 (H3N2) virus is now underway.